Surgical staplers greatly facilitate surgical procedures by permitting simultaneous application of rows of staples (in effect, suturing tissue) and cutting of tissue between adjacent rows of staples. Such devices typically include cooperating jaw members, one of which includes a staple-filled cartridge, and the other in the form of a staple anvil against which the staples are driven for deforming the legs of the staples, thereby effecting "suturing" of tissue positioned between the jaw members. Such staplers typically include one or more wedge-shaped cams which are operated to drive the staples against the anvil. When cutting of tissue is desired, these devices further include a tissue-cutting knife blade which is advanced between adjacent rows of staples.
Surgical staplers such as described above are disclosed in U.S. Pat. No. Re. 34,519, to Fox et al., U.S. Pat. No. 5,129,570, to Schulze et al., U.S. Pat. No. 4,955,959, to Tompkins, U.S. Pat. No. 5,040,715, to Green et al., and U.S. Pat. No. 5,307,976, to Olson et al., all of which are hereby incorporated by reference.
For endoscopic surgical procedures, an endoscopic surgical stapler such as disclosed in the above-referenced U.S. Pat. No. 5,307,976 can be employed. In such a device, the staple-filled cartridge and associated cooperating anvil are positioned at the distal end of a generally elongated endoscopic portion, which portion extends from a frame including a handle portion. The handle portion is grasped by the surgeon, with one or more operating levers, or like elements, provided at the handle portion for effecting the desired surgical steps. For example, in a typical construction, a first operating lever is operatively connected with the anvil of the stapler for moving the anvil toward the associated staple cartridge to grip and clamp tissue therebetween, with a second operating lever provided for thereafter driving the staples from the cartridge against the anvil.
Experience has shown that it can sometimes be difficult for a surgeon to judge the thickness of tissue being clamped between the staple cartridge and the anvil, and as a result, the forces generated in the operating levers and linkages of the stapler can vary. In some instances, relatively high forces can be created in the linkages and levers of the stapler, particularly in a construction such as disclosed in U.S. Pat. No. 5,040,715, wherein both of the operating levers of a surgical stapler are mounted on a common pivot pin. Also, it is often the case that the force to clamp tissue is significantly higher than the force to form staples and cut tissue, so the pivots of each of the operating levers need not be equally robust. However, it is desirable ergonomically to have the levers situated in the same area on the handle for the user to operate these levers more comfortably. In such a construction, the combined loads of both operating levers acting on a common pivot pin can create undesirably high stresses in tile pivot pin. The present invention is directed to an improved arrangement for mounting the operating levers on the associated frame of the stapler for accommodating the varying forces which can be encountered attendant to varying surgical conditions, while assuring precise and convenient control of the instrument by the surgeon.